HomeMy WebLinkAboutPAVILION SHOPPING CENTER (4366 S. COLLEGE) WTF - PDP/FDP - 21-00 - SUBMITTAL DOCUMENTS - ROUND 1 - WTE / WTF INFORMATIONinformation, and sophisticated analytical tools to ensure that we maintain our
unblemished record for quality.
I trust this letter satisfies your requests. If you have additional questions or comments, I
may be reached at (503) 315-4515.
Sincerely,
<-
Adrian McJunkin, P.E.
Communications Division p REj
Pole Engineering Team Leader QP....• (,S'T�,ts
Page 3 of 3
For instance, this monopole will be designed for an 85 mph Basic Wind Speed. This
Basic Wind Speed translates into a sustained, gusted wind speed of 118 mph at the top of
the monopole. Considering a survivable wind speed which considers the ultimate yield
strength of the steel, failure of the monopole would not be expected until wind speeds
exceeded 132 mph. Beyond 132 mph we can only make an educated guess as to the
failure mechanisms that would take place. The term Failure used above only suggests
that "local buckling" has occurred at this point. "Local Buckling" is the result of a
relatively small portion of the shaft distorting by "kinking" the steel. Local Buckling
does not cause a free falling pole, rather it redistributes the stresses toward the remaining
portion of the cross section that has unused capacity. If wind speeds continue to increase,
the pole may continue to buckle and eventually crumple/fold over upon itself. Once this
takes place, a significant reduction in wind load will cause the pole not to experience
further deformations.
In the above scenerio, we are assuming sustained, gusted winds. In reality, a gust would
soon dissipate and, after this peak wind is gone, the stress in the pole would be reduced.
Poles are flexible, forgiving structures which are not generally susceptible to damage by
impact loads such as a wind gust or earthquake shocks. It may take some time for the
entire structure to "see" the impact loading. Even after a local buckle, the pole has
significant capacity. It is this capacity along with the transitory nature of the loading that
prevents a pole from "falling over." It should also be noted that typical antennas are
designed to survive 125 mph. With the absence of antenna loading the pole would have
additional capacity.
Valmont/Microflect's Pole design and full-scale testing have provided the public with a
very reliable product. Poles have gone through extensive full scale testing, resulting in a
history of being extremely reliable. This public, in my opinion, has been well served.
Valmont/Microflect has provided structures that have performed well during the
earthquakes in California, the hurricanes in the South (including Hugo, Andrew,
and Opal), and a number of tornadoes. Valmont/Microflect has never experienced
an in service failure of a communication pole due to weather induced overloading,
even though, as in the cases of Hurricane Hugo and Hurricane Andrew, the wind
speeds may have exceeded the design wind speed.
Valmont/Microflect has no direct experience with monopole failures. However, from
what evidence we have seen from other vendor's experiences, I can state that it is rare for
a monopole to fall in a radius larger than, say, half it's height, and that in most cases it
will collapse in a small confined area as it comes down upon itself.
Valmont/Microflect's communication towers have proven to be very reliable products. In
our over 40 years of engineering and fabricating thousands of towers and monopoles, we
have not had one structure fail due to overloading (even in the extreme cases that wind
speeds have exceeded design values). We use the latest standards, wind speed
Page 2 of 3
valmont T
MICROFLECT
City of Ft. Collins
Current Planning Department
281 N. College Ave.
P.O. Box 580
Ft. Collins, CO 80522-0580
July 27, 2000
Subject: Failure Modes for Tapered Monopoles and Mounting Appurtenances.
Nextel Site No. CO-0392B Ft. Collins, CO - Proposed 80' Monopole
To Whom It May Concern:,
We understand that there is some concern on the part of local building officials regarding
the potential for failure of proposed 80' tapered monopole we will be quoting for the
above site. To address this concern we offer the following:
Communications monopole structures designed by Valmont/Microflect are typically sized
in accordance with the latest revision of the EIA/TIA 222 Standard entitled "Structural
Standards for Steel Antenna Towers and Antenna Supporting Structures." This standard
has been approved by ANSI, who has generated the standard for "Minimum Design
Loads for Buildings and Other Structures". The standard, which is the basis for design
loading for practically every building code and standard in the country, has dealt with the
design of antenna support structures for over 40 years. The EIA standard, based on
provisions of this nationally known specification, has a long history of reliability. At its
core philosophy is it's first and foremost priority to safeguard and maintain the health and
welfare of the public.
The EIA standard dictates minimum wind loading (the predominant loading on a
monopole structure) for each county in the United States. It is Valmont/Microflect's
policy to use the wind loading listed in the latest EIA standard as a minimum loading
unless the customer specifies a larger value. Statistically, the wind speed listed in the
EIA standard has been determined to be that wind which has an average reoccurrence of
50 years (i.e. the magnitude has a 2% chance of occurring in any one year). This wind is
the "fastest mile" wind at 33 ft. above ground. By definition, the "fastest mile" wind is
the average velocity of a mile of wind passing a fixed point. This "fastest mile" wind is
customized with height, exposure, and gust factors that apply to a particular installation
which, in effect, increases the wind velocity.
The loads generated by this wind speed, along with weight of the monopole sections and
any ice loading being considered, are used to design the structural system. To fail
monopole sections, the wind must exceed all of our estimates for magnitude, duration, as
well as overcome the factor of safety determined from the design.
Communications Division, Valmont Industries, Inc. 3575 25th Street SE Salem, Oregon 97302-1123 USA
Page 1 of 3 503.363.9267 Fox 503.363.4613 www.valmont.com